Infusion device and driving mechanism and process for same with actuator for multiple infusion uses

ABSTRACT

A drive mechanism for delivery of infusion medium a coil capable of being electrically activated to provide an electromagnetic field. The coil surrounds a piston channel extending in an axial direction. An armature is located adjacent the coil, on one side of the axial channel. The armature is moveable toward a forward position, in response to the electromagnetic field produced by activation of the coil. A piston is located within the piston channel and is moveable axially within the channel to a forward position, in response to movement of the armature to its forward position. The armature and piston are moved toward a retracted position, when the coil is not energized. The armature may be configured with a reduced diameter by including a coil cup for supporting the coil including a shelf portion defining at least a portion of a pole surface of the coil cup.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a Continuation of U.S. application Ser. No.10/925,065, filed Aug. 23, 2004, incorporated herein by reference in itsentirety, which is a Division of U.S. application Ser. No. 10/331,132,filed Dec. 26, 2002, incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to infusion devices, systems andprocesses and, in particular embodiments to infusion devices, systemsand processes employing a drive mechanism configuration having anactuator configured for improved efficient operation with a variety oftypes of infusion media. Further embodiments of the invention relate todrive mechanisms for such infusion devices and systems, and processes ofmaking and using such drive mechanisms.

BACKGROUND

Infusion devices are typically used to deliver infusion media, such asmedication, to patients. An implantable infusion device is designed tobe implanted in a patient's body, to administer an infusion medium tothe patient at a regulated dosage. An external infusion device isdesigned to be located outside of the patient's body and connected tothe patient by a suitable catheter, tubing or the like, to administer aninfusion medium into the patient's body.

Both implantable and external infusion devices may include one or morepump drive mechanisms for creating pumping forces to cause or helpdelivery of infusion media to the patients. Various types of pump drivemechanisms with electromagnetic drive devices have been developed forsuch infusion devices. Such pump drive devices typically include anelectromagnetic actuator having an armature portion made of amagnetically conductive material. The armature interacts,electromagnetically, with an electrical coil housed in a coil cup madeof magnetically conductive material. Such drive mechanisms include, forexample, the drive mechanisms described in U.S. patent applicationentitled “Infusion Device and Driving Mechanism For Same,” Ser. No.10/033,722, filed Dec. 27, 2001, by the owner of the present invention.Other pump drive mechanisms having electromagnetic armature-coilassemblies include, for example, those described in U.S. Pat. No.4,594,058 to Fischell; U.S. Pat. No. 4,684,368 to Kenyon; U.S. Pat. No.4,569,641 to Falk et al.; U.S. Pat. No. 4,568,250 to Falk, et al.; U.S.Pat. No. 4,636,150 to Falk, et al.; and U.S. Pat. No. 4,714,234 to Falket al.

Pump drive mechanisms for infusion devices (including those referencedabove) may include components, such as actuators, that come into directcontact with the infusion medium during normal operation. In suchinfusion devices, the chemical interaction of the infusion medium withmaterials used for such components may have an adverse effect on thepatient to which the infusion medium is administered. The risk of suchan adverse effect may be greater for implantable infusion devices, wherecomponents of an infusion pump may remain in contact with infusionmedium over a prolonged period of time inside of an implanted device.For example, contact with the armature may cause leaching or otherinteractions of materials between the infusion medium and the armature.Such interactions may adversely alter the medical effect of the infusionmedium on the patient. Prolonged contact may cause other detrimentaleffects, such as corrosion of the armature.

Pump drive mechanisms may be manufactured for use with a particular,known infusion medium, in which case, the effect (and prolonged effect)of direct contact of that particular infusion medium on components ofthe pump drive mechanism may be studied in advance. With such studies,the materials and components of the infusion pump may be selected anddesigned to be in contact with the infusion medium, yet, have a suitablybenign effect on the patient. However, if the particular type ofinfusion medium is not known at the time of manufacture of the pumpmechanism, for example, in the case in which a pump mechanism is beingmanufactured for multiple possible infusion uses, the ability to studyeffects on all possible infusion media may not be practical or possible.Accordingly, there is a demand in the industry for a pump mechanism andprocess that is suitable for multiple possible infusion uses.

In some contexts of use, the infusion device must be operable for anextended period with a limited power supply. For example, batterypowered infusion devices may be implanted in or otherwise connected topatients, to deliver medication at controlled intervals over a prolongedperiod of time. A battery replacement in an implanted device may requiresurgery on the patient to remove and re-implant the device. Accordingly,there is a demand in the industry for infusion devices which makeefficient use of power supplies and, thus, require fewer or no powersupply replacements.

Because implantable infusion devices are designed to be implanted in thepatient's body, the dimensions of such devices can have an impact on thedetermination of the location in the body at which a device may beimplanted, the level of comfort of the implant patient and the externalappearance of the implant site. Typically, a device with relativelysmall dimensions and, in particular, a relatively small thickness formfactor, will provide greater flexibility in the choice of location inthe patient's body to place the implant and will minimize patientdiscomfort and minimize noticeable protrusions at the implant site.Accordingly, there is a demand in the industry for minimizing theoverall dimensions, and, in particular, the thickness dimension ofimplantable infusion device.

SUMMARY OF THE DISCLOSURE

Accordingly, embodiments of the present invention relate to infusiondevices and drive mechanisms for infusion devices which address one ormore of the above-mentioned industry demands.

Embodiments of the invention relate to such devices and drive mechanismsconfigured for use with any one of multiple different infusion media.

Further embodiments relate to such devices and drive mechanismsconfigured and operated to make highly efficient use of electrical powerto prolong operational life.

Further embodiments of the invention relate to such devices and drivemechanisms configured for implantation in a patient's body and, thus,configured to have a relatively small thickness dimension, for example,to minimize trauma to the implant recipient (referred to herein as thepatient). However, aspects of the invention may apply to externalinfusion devices and drive mechanisms for such external devices and,thus, other embodiments of the invention relate to such externalinfusion devices and drive mechanisms.

An implantable infusion device according to an embodiment of theinvention includes a housing made from a biocompatible and infusionmedium compatible material. The infusion device housing contains areservoir for holding a volume of infusion medium, such as, but notlimited to, a medication to be administered to the patient. The infusiondevice housing has an outlet through which the infusion medium may beexpelled.

The infusion device further includes a drive mechanism having an inletcoupled in fluid flow communication with the reservoir and an outletcoupled in fluid flow communication with the infusion device housingoutlet. The drive mechanism employs electromagnetic and mechanicalforces to move an actuator piston between retracted and forwardpositions or states, to cause infusion medium to be drawn from thereservoir, through an inlet and forced out of an outlet.

A drive mechanism, according to one embodiment, comprises an assembly ofcomponents which may be manufactured and assembled in a relatively costefficient manner. The components include a housing containing a coildisposed within a coil cup and a piston channel surrounded by the coil.The components also include an actuator having a piston extendingthrough the piston channel and an armature disposed at one end of thepiston channel. A piston chamber, outlet chamber and outlet valve arelocated at the other end of the piston channel.

According to embodiments of the present invention, the coil cup may becomposed of a magnetizable material and may include a generally annularouter wall, the outer wall having a generally annular shelf portionextending from the outer wall towards the inner wall. The shelf portionhas an end defining an outer pole surface of the coil cup. In oneembodiment of the present invention, the inner wall of the coil cupincludes a generally annular shelf portion extending from the inner walltowards the outer wall. The shelf portion has an end defining at least aportion of an inner pole surface of the coil cup. The coil cup includesa generally annular interior between the outer and inner walls. Theannular interior contains a coil.

When the coil is in a quiescent state, the armature and piston are urgedtoward a retracted position by mechanical or magnetic forces. When thecoil is energized, the armature and piston move to a forward strokeposition. The movement of the piston from a retracted position to aforward position creates pressure differentials within the drivemechanism to drive medium out the outlet. Mechanical force may returnthe piston to the retracted position. The movement of the piston from aforward position to a retracted position creates pressure differentialsto draw medium into the drive mechanism inlet and into the pistonchamber.

Various types of electromagnetic actuator type drive mechanisms forinfusion devices have been configured with actuators having an armatureportion made of a magnetically conductive material. The armatureinteracts, electromagnetically, with an electrical coil housed in a coilcup made of magnetically conductive material. An example of a pump drivemechanism suitable for an implantable infusion device is described inU.S. patent application entitled “Infusion Device and Driving MechanismFor Same,” Ser. No. 10/033,722, filed Dec. 27, 2001, by the owner of thepresent invention. Certain embodiments of the present invention includea pump drive mechanism as described in U.S. patent application Ser. No.10/033,722, but with differences relating to the actuator and/or coilcup configuration and operation as described herein. Other embodimentsmay employ other suitable pump drive mechanisms having actuator and/orcoil cup aspects as described herein.

As described in further detail below, armature portions of actuatorsemployed in embodiments of the present invention may be configured witha reduced diameter, for example, to reduce fluidic resistance toactuator movement. Alternatively, or in addition, further embodiments ofthe present invention employ an armature structure that is free ofapertures (or employs a reduced number of apertures as compared toactuators described in U.S. patent application Ser. No. 10/033,722) and,thus, may be provided with a protective layer or coating in a simplifiedmanufacturing process.

Other embodiments may employ an armature that may be manufactured fromany suitable material, including materials having a low magneticpermeability. According to these embodiments, the armature portion ofthe actuator may be formed with a cavity into which a material having arelatively high magnetic permeability may be placed. These materials maybe, for example, ferrous materials.

Alternatively, or in addition, actuators according to furtherembodiments of the invention employ a piston portion that has a centralchannel and valve structure for increasing the flow rate of infusionmedium into a pumping chamber and inhibiting backflow of infusion mediumfrom the pumping chamber. In yet further embodiments, the diameter ofthe piston portion may be reduced and/or the diameter of the pistonchannel in which the piston moves may be increased, to increase the flowrate of infusion medium into the pumping chamber. By accommodating anincreased flow rate, the drive mechanisms may be operable with a greatervariety of infusion media.

Embodiments of the invention may employ a coaxial arrangement of thepiston, the piston channel and the coil, to provide significantadvantages with respect to providing a relatively thin form factor andefficient power usage. A number of features described herein and in U.S.patent application Ser. No. 10/033,722 can each provide or be combinedto contribute to a reduction in the thickness form factor of the drivemechanism. For example, a coaxial arrangement of components can beimplemented with a smaller thickness form factor than alternativearrangements in which components are arranged in series with each otherin the thickness dimension. Embodiments may include an inlet volume orchamber on one side of the coil and an outlet chamber on the oppositeside of the coil, with a flow passage through the piston channel, suchthat the coil and flow channel share a common portion of the thicknessdimension. The armature may be located within the inlet volume and,thus, share a common portion of the thickness dimension with the inletvolume. The outlet chamber may be centrally located within the samehousing that has the coil cup and formed in relatively close proximityto the coil cup in the thickness dimension of the housing.

In addition, a number of features described herein and in U.S. patentapplication Ser. No. 10/033,722 can provide, or be combined tocontribute to, the efficient use of power to, prolong the operationallife of the drive mechanism.

These and other aspects and advantages of the invention will be apparentto one of skill in the art from the accompanying detailed descriptionand drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings in which like reference numbers representcorresponding parts throughout:

FIG. 1 is a perspective view of an implantable infusion device accordingto an embodiment of the invention.

FIG. 2 is a perspective view of a drive mechanism for an implantableinfusion device according to an embodiment of the invention.

FIG. 3A is a cross-section view of one example embodiment of the drivemechanism of FIG. 2, in a retracted position or state.

FIG. 3B is a cross-section view of one example embodiment of the drivemechanism of FIG. 2, in a retracted position or state.

FIG. 3C is a cross-section view of one example embodiment of the drivemechanism of FIG. 2, in a retracted position or state.

FIG. 3D is a cross-section view of one example embodiment of the drivemechanism of FIG. 2, in a retracted position or state.

FIG. 4A is a cross-section view of the example drive mechanismembodiment of FIG. 3A, in a forward stroke position or state.

FIG. 4B is a cross-section view of the example drive mechanismembodiment of FIG. 3B, in a forward stroke position or state.

FIG. 4C is a cross-section view of the example drive mechanismembodiment of FIG. 3C, in a forward stroke position or state.

FIG. 4D is a cross-section view of the example drive mechanismembodiment of FIG. 3D, in a forward stroke position or state.

FIG. 5 is a an exploded view of an embodiment of the drive mechanismshown in FIGS. 3A-D and 4A-D.

FIG. 6 is a perspective view of an embodiment of a housing member forthe drive mechanism in FIGS. 3A-D and 4A-D.

FIG. 7A is a perspective view of an embodiment of a coil cup for thedrive mechanism having an outer shelf.

FIG. 7B is a perspective view of an embodiment of a coil cup for thedrive mechanism having an inner shelf.

FIG. 7C is a perspective view of an embodiment of a coil cup for thedrive mechanism having both an outer and inner shelf.

FIG. 8 is a perspective view of an embodiment of an actuator comprisingan armature and a piston for the drive mechanism in FIGS. 3A-D and 4A-D.

FIG. 9 is a simplified cross-section diagram, showing an arrangement ofan actuator member and coil cup member for the drive mechanism in FIG.3A.

FIG. 10 is a simplified cross-section diagram, showing anotherembodiment of an actuator comprising an armature and a piston for adrive mechanism of the type shown in FIGS. 3A-D and 4A-D.

FIG. 11 is a simplified cross-section diagram, showing anotherembodiment of an actuator comprising a 2-piece structure having anarmature and a piston, for a pump drive mechanism.

FIG. 12 is a simplified cross-section diagram, showing yet anotherembodiment of an actuator comprising an armature and a piston for adrive mechanism of the type shown in FIGS. 3A-D and 4A-D and including avalve structure on one end of the piston.

FIG. 13 is a detailed view of an embodiment of a valve structure shownin FIG. 12.

FIG. 14A is a simplified cross-section diagram, showing an unassembledarmature according to embodiments of the present invention.

FIG. 14B is a simplified cross-section diagram, showing an assembledarmature according to embodiments of the present invention.

FIG. 15 is a simplified cross-section diagram, showing an assembledactuator including an armature and a piston, according to embodiments ofthe present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The following detailed description is of the best presently contemplatedmode of implementing the invention. This description is not to be takenin a limiting sense, but is made merely for the purpose of illustratingthe general principles of embodiments of the invention. The scope of theinvention is best defined by the appended claims.

As discussed above, the present invention relates generally to infusiondevices having drive mechanisms and also to drive mechanismconfigurations for infusion of a medium into a patient or otherenvironment. Embodiments of the invention relate to such devices anddrive mechanisms configured for use with any one of multiple differentinfusion media.

Embodiments of the invention relate to such devices and drive mechanismsconfigured for implantation in a patient's body. Embodiments describedherein allow the drive mechanism for such infusion device to have arelatively small thickness dimension, for example, to minimize trauma tothe implant recipient (referred to herein as the patient). Furtherpreferred embodiments relate to such devices and drive mechanismsconfigured and operated to make highly efficient use of electrical powerto prolong operational life in an implant environment. However, becauseaspects of the invention may be applied to external infusion devices aswell, yet further embodiments of the invention relate to such externalinfusion devices and drive mechanisms for such external devices.

FIG. 1 shows an implantable infusion device 10 according to anembodiment of the invention. The illustrated device 10 is configured tobe surgically implanted into a patient, for example, in the abdominalregion, between the skin and the abdominal wall. A catheter connected tothe pump may deliver infusion medium to the patient, for example, byfeeding infusion medium to a particular location in the venous system,in the spinal column, in the peritoneal cavity, or in another suitablelocation of the patient.

Preferred embodiments of the device 10 are configured in accordance withone or more aspects of the invention for enhancing operability withmultiple types of infusion media, enhancing power usage efficiency andsimplifying implantation. As noted above, further embodiments of theinvention may be implemented as external infusion devices, which connectto patients through suitable catheter devices or the like. Yet furtherembodiments of the invention may be used in other contexts, for deliveryof a medium into other suitable environments. Therefore, for purposes ofsimplifying the present disclosure, the term “patient” is used herein torefer to the entity or environment in which an implantable device isimplanted or to which an external device is connected, whether or notthe implant or connection is carried out for medical purposes. Also, theterm “infusion medium” is used herein to refer to any suitable mediumdelivered by the drive device.

The device 10 in FIG. 1 includes a generally disc-shaped housing 12.While a generally circular disc-shaped embodiment is illustrated in FIG.1, further embodiments of the invention may employ housings of othershapes, including, but not limited to, oval, oblong, rectangular, orother curved or polygonal shapes. The housing 12 has a diameterdimension D, defining the diameter of the disc shape, and a maximumthickness dimension T, defining the maximum thickness of the device.

In implantable device embodiments, the housing 12 preferably is made ofa biocompatible material, is hermetically sealed from the externalenvironment and has a relatively small or minimized thickness dimensionT, to reduce or minimize patient trauma during implant surgery and afterimplantation. For example, the housing 12 may be made from titanium,titanium alloy, stainless steel or other biocompatible materials and maybe configured to provide a hermetically sealed environment for some orall of the components within the interior of the housing.

The housing 12 includes a reservoir housing portion 13 containing areservoir for holding a volume of infusion medium, such as, but notlimited to, a liquid medication to be administered to the patient. Thehousing 12 includes a further housing portion 14, located above thereservoir housing portion 13 in the orientation shown in FIG. 1, forcontaining a drive mechanism 20, a power source and control electronics22 described below.

Representative examples of reservoir housing portions and reservoirswhich may be employed in embodiments of the invention are described inco-pending U.S. patent application Ser. No. 10/033,377 (attorney docketno. 047711.0287), titled “Implantable Infusion Device And Reservoir ForSame,” which is incorporated herein by reference. However, furtherembodiments may employ other suitable reservoir configurations,including, but not limited to, those described in U.S. Pat. No.5,514,103 and U.S. Pat. No. 5,176,644, each to Srisathapat et al, U.S.Pat. No. 5,167,633 to Mann et al., U.S. Pat. No. 4,697,622 to Swift andU.S. Pat. No. 4,573,994 to Fischell et al.

The housing 12 also has an outlet 16 through which the infusion mediummay be expelled. When the device 10 is implanted in a patient orconnected externally to a patient, a catheter may be connected to theoutlet 16, to deliver infusion medium expelled from the outlet 16 intothe patient's blood stream or to a selected location in the patient'sbody. The infusion device 10 may also include an inlet structure 18which provides a closeable and sealable fluid flow path to the reservoirin the reservoir portion 13 of the housing. In an example embodiment,the inlet structure provides a port for receiving a needle through whichfluid may be transferred to the infusion device, for example, to fill orre-fill the reservoir of the device. The inlet structure may beconfigured to re-seal after a fill or re-fill operation, to allowmultiple re-fill and re-seal operations.

One example of an inlet structure is described in co-pending U.S. patentapplication Ser. No. 10/034,628 (attorney docket no. 047711.0286),titled “Infusion Device And Inlet Structure For Same,” which isincorporated herein by reference. However, further embodiments mayemploy other suitable inlet structures, including, but not limited to,those described in U.S. Pat. No. 5,514,103 and U.S. Pat. No. 5,176,644,each to Srisathapat et al, U.S. Pat. No. 5,167,633 to Mann et al., U.S.Pat. No. 4,697,622 to Swift and U.S. Pat. No. 4,573,994 to Fischell etal.

As described above, preferred embodiments of the device 10 areconfigured in accordance with one or more aspects of the invention forenhancing operability with multiple types of infusion media. In suchembodiments, any one of various types of infusion media having differentcompositions, concentrations and/or chemical characteristics may becontained, filled or re-filled into the reservoir for a given infusiontreatment program. Thus, in such embodiments, the components of thereservoir, inlet and outlet structures that come into contact with theinfusion medium may be made with (or coated with) a suitable materialthat will minimize the risk of having an adverse reaction with a any ofthe multiple types of infusion media that may be contained in thereservoir. Suitable materials may include, but are not limited to,titanium, titanium alloy, stainless steel or the like.

The infusion device 10 includes a drive mechanism 20, such as a pump,and an electronic control system 22 located in the housing portion 14.The drive mechanism 20 is connected between the reservoir and the outlet16. The electronic control system 22 includes a power source, such as abattery, and control electronics for controlling the drive mechanism 20to deliver infusion medium from the reservoir, to the patient in aselected manner. The drive mechanism may be controlled to deliverinfusion medium in any suitable manner, for example, according to aprogrammed dispensing rate or schedule, according to an actuation signalfrom a sensor, timer, manual actuator or other suitable source, orcombinations thereof.

The programmed dispensing rate or schedule may be different fordifferent types of infusion media. Thus, the control system 22 mayinclude programmable electronics which allow programming of dispensingfunctions, including rate, schedule, dispensing time, dispensing period,sensor activities that trigger dispensing and the like, depending uponthe type of infusion medium contained in the reservoir. Such programmingmay be accomplished prior to implantation. In other embodiments,programming may be accomplished by a wireless communication link, afterimplantation. Systems for wireless communication between controlelectronics of an implanted infusion device and an external programmingdevice are described in U.S. patent application Ser. No. 10/033,530,titled “Safety Limits for Closed-Loop Infusion Pump Control”, filed Dec.26, 2001, which is owned by the owner of the present invention.

An example of a pump drive mechanism suitable for an implantableinfusion device is described in U.S. patent application entitled“Infusion Device and Driving Mechanism For Same,” Ser. No. 10/033,724,filed Dec. 27, 2001, by the owner of the present invention andincorporated herein by reference. Certain embodiments of the presentinvention include a pump drive mechanism 20 similar to that described inU.S. patent application Ser. No. 10/033,722, but with differencesrelating to the actuator and/or coil cup configuration and operation asdescribed herein. Other embodiments may employ other suitable pump drivemechanisms having actuator and/or coil cup aspects as described herein.

The pump drive mechanism described in U.S. patent application Ser. No.10/033,724 employs an actuator having an armature portion that is formedwith a plurality of apertures and radial rib sections. The aperturesallow the armature portion to move in a volume of fluidic infusionmedia, with reduced fluidic resistance. This is accomplished, byallowing infusion media to pass through the apertures as the armatureportion moves back and forth between forward and retracted positions.The radial ribs provide radial paths for electromagnetic flux betweenthe pole surfaces of the armature. However, an armature structure thathas a plurality of apertures and radial rib portions may be difficult tolayer with a protective material or coating. It can be difficult tolayer or apply coatings to all exposed surfaces formed by the aperturesand ribs.

Accordingly, embodiments of the present invention employ an armaturestructure that is free of apertures (or employs a reduced number ofapertures as compared to actuators described in U.S. patent applicationSer. No. 10/033,722) and, thus, may be readily provided with aprotective layer or coating in a simplified manufacturing process. Sucharmature portions may be configured with a reduced diameter, forexample, to reduce fluidic resistance to actuator movement. Furtherembodiments of the invention employ an armature structure with apertures(as described in U.S. patent application Ser. No. 10/033,722), but witha reduced diameter, for example, to reduce fluidic resistance to motionand improve power usage efficiency.

Alternatively, or in addition, actuators according to furtherembodiments of the invention employ a piston portion that has a centralchannel and valve structure for increasing the flow rate of infusionmedium into a pumping chamber and inhibiting backflow of infusion mediumfrom the pumping chamber. In yet further embodiments, the diameter ofthe piston portion may be reduced and/or the diameter of the pistonchannel in which the piston moves may be increased, to increase the flowrate of infusion medium into the pumping chamber. By accommodating anincreased flow rate, the drive mechanisms may be operable with a greatervariety of infusion media.

The drive mechanism 20 includes mechanical and electromagneticcomponents that inherently inhabit a volume of space within the housing12. In that regard, the drive mechanism 20 can contribute to thethickness requirements of the housing 12 and, thus, to the overallthickness dimension T of the device 10. Preferred embodiments of thepresent invention relate to and employ drive mechanism configurationsthat reduce or minimize the thickness requirements of the device,without compromising drive capabilities.

The above-referenced U.S. patent application Ser. No. 10/033,722describes features relating to the ability to reduce or minimize thedevice thickness dimension T, without compromising the drivecapabilities. Such features can provide significant advantages withrespect to patient comfort, appearance and flexibility in selectingimplant locations in the body. Embodiments of the present invention mayemploy one or more of such features, in conjunction with other aspectsof the actuator and coil cup configurations described herein forimproving operation with any one of multiple types of infusion media inan implant environment.

Also in further embodiments, the device 10 is configured such that, onceimplanted, it functions for a relatively long period of time toadminister infusion medium to the patient and periodically bereplenished from outside of the patient's body. The operational life ofthe device 10 is, however, limited in part by the capacity of its powersource and the power requirements of the device. Preferred embodimentsof the device 10 employ drive mechanisms, as described below, thatprovide reliable pumping action and are highly efficient with respect topower consumption, to improve the operational life of the device 10.Alternatively or in addition, drive mechanisms that provide highlyefficient use of power, as described below, may be operated with smallerpower sources (for example, smaller batteries) which can allow thedevice 10 to be made smaller.

One manner of lowering the power consumption requirements of the device10 is to employ a coaxial coil and piston pump configuration and one ormore features described herein and in U.S. patent application Ser. No.10/033,722, for making highly efficient use of electromagnetic energy.Another manner of lowering the power consumption requirements of thedevice 10 is to reduce the number of operations of the drive mechanism20 required over a given period of time, by pumping reduced volumes of ahigher concentration infusion medium (an infusion medium with a higherconcentration of active ingredients) or pumping higher concentrationvolumes at reduced intervals. However, higher concentration mediums mayrequire a greater precision in controlling the volume delivered to thepatient during a drive operation, to avoid delivering too great or toosmall of a volume of the higher concentration medium to the patient.Accordingly further preferred drive mechanisms 20 are configured withone or more features described herein to allow delivery of controlledvolumes of infusion medium and, thus, to allow sufficiently precisedelivery of relatively high concentration infusion medium.

Drive Mechanism Embodiment

FIG. 2 shows a drive mechanism 20 according to an example embodiment ofthe present invention. In the illustrated embodiment, the example drivemechanism 20 has a partially cylindrical, disc-shaped configuration withan inlet 26 and an outlet 28. The inlet 26 may be connected in flowcommunication with the reservoir portion 13 of the device 10 in FIG. 1,through suitable conduit (not shown) within the device 10. Similarly,the outlet 28 may be connected in flow communication with the outlet 16of the device 10 in FIG. 1, through suitable conduit (not shown) withinthe device 10.

FIGS. 3A-D shows cross-sectional views of embodiments of the drivemechanism 20, in a retracted position or state. FIG. 4A-D showcross-sectional views of the same drive mechanism 20 embodiment, in aforward position or state. As described in more detail below, the drivemechanism 20 employs electromagnetic and mechanical forces to change (ormove) between retracted and forward states, to cause infusion medium tobe drawn in through the inlet 26 and forced out of the outlet 28.

The drive mechanism 20, according to one embodiment, comprises anassembly of components as shown in an exploded view in FIG. 5. Suchcomponents include a housing member 30, a coil cup 32, an electricallyconductive coil 34, an actuator member 36, a cover member 38 and variousother components that are described in further detail below. Some ofthose components are also shown in perspective views in FIGS. 6-8 andare described in more detail below.

The pump drive mechanisms 20 described herein may include, for example,various components that correspond in structure and operation to similarcomponents of the drive mechanism described in U.S. patent applicationentitled “Infusion Device and Driving Mechanism For Same,” Ser. No.10/033,722, filed Dec. 27, 2001, by the owner of the present invention.However, pump drive mechanisms 20 described herein employ uniqueconfigurations relating to the actuator member 36, coil cup member 32and related components. Such unique component configurations may beemployed, for example, to improve the ability of the pump drivemechanism to operate with any one of a variety of types of infusionmedia, to minimize fluid stirring and fluidic resistance to actuatormotion during a pump stroke and/or to simplify manufacturing processes.

While certain embodiments of the present invention employ a pumpmechanism that is configured similar in many respects to pump mechanismsdescribed in U.S. patent application Ser. No. 10/033,722, aspects of thepresent invention may be applicable to other pump mechanismconfigurations that employ an actuator and coil cup arrangement.Accordingly, other embodiments may employ other suitable pump mechanismconfigurations.

Housing Member for Drive Mechanism

The housing member 30 according to an example embodiment of theinvention (shown in perspective view in FIG. 6) is open on one side to ahollow, annular interior section 40. The housing member 30 has a centralhub portion 42 with a central piston channel 44. The bottom side of thehousing member 30 (with reference to the orientation shown in FIGS. 3A-Dand 4A-D), includes an opening 46 to the hollow interior section 31,through which coil wires or connection leads may pass. The bottom sideof the housing member also includes a configuration of recesses andcavities for providing an outlet chamber (48 in FIGS. 3A-D and 4A-D), anoutlet passage and, in some embodiments, accumulator chambers asdescribed in the above-referenced U.S. patent application Ser. No.10/033,722. The housing member 30 is preferably made of a generallyrigid, biocompatible and infusion medium compatible material, having noor low magnetic permeability such as, but not limited to, titanium,stainless steel, biocompatible plastic, ceramic, glass or the like.

Coil Cup Member For Drive Mechanism

As shown in FIGS. 3A-D and 4A-D, the coil cup member 32 is locatedwithin the annular interior section of the housing 30. Perspective viewsof example embodiments of a coil cup 32 are shown in FIGS. 7A, 7B and7C. The example coil cup member 32 has a generally cylindrical shape,with an opening 50 one side to a hollow, annular interior. The coil cupmember 32 includes a central hub portion 51 having a central channel orbore 52 located axial relative to the annular interior. The hub portion51 of the coil cup member defines an end surface 54 (or inner polesurface).

The coil cup member 32 has an outer peripheral wall 56 connected to thehub portion 51 by a backiron portion 57 of the coil cup member. In theembodiment illustrated in FIG. 3A and FIG. 7A, the coil cup member 32also includes an annular lip or shelf 58 that extends from the outerwall 56, toward the hub portion 51, to cover a portion of the hollowinterior of the coil cup member. The annular opening 50 is providedbetween the hub 51 and an annular, free edge of the shelf 58. The shelf58 has a surface 59 (or outer pole surface) facing away (and upward inFIG. 7A) from the hollow interior of the coil cup member 32. Asdescribed below, the shelf 58 allows the actuator 36 to be configuredwith a relatively small diameter armature portion. By minimizing thediameter of the armature portion, the configuration of the armature maybe simplified, thus simplifying manufacturing processes, stirring ofinfusion media during actuator movement may be reduced and the powerusage for moving the actuator may be more efficient.

In an alternative embodiment illustrated in FIG. 7B, the coil cup member32 may include an annular lip or shelf 98 that extends from the hubportion 51 toward the outer wall 56. The annular opening 50 is providedbetween the annular, free edge of the shelf 98 and the outer wall 56.The shelf 98 has a surface 99 (extending the inner pole surface 54 (seeFIG. 7A)) facing away (and upward in FIG. 7B) from the hollow interiorof the coil cup member 32. The embodiment of the coil cup member 32shown in FIG. 7B may be employed with an actuator member as described inU.S. patent application Ser. No. 10/033,722. Thus, while there is noreduction in the diameter of the armature structure according to thisembodiment, shelf 98 provides a larger pole area of the coil cup member32 to increase electromagnetic flux between the pole surfaces of thecoil cup member 32 and the pole surfaces of the armature.

In an alternative embodiment illustrated in FIG. 3B and FIG. 7C, thecoil cup member 32 may include both an annular lip or shelf 58 thatextends from the outer wall 56, toward the hub portion 51 and an annularlip or shelf 98 that extends from the hub portion 51 toward the outerwall 56. The annular opening 50 is provided between the annular, freeedge of the shelf 98 and the annular, free edge of the shelf 58. Theshelf 58 has a surface 59 (or outer pole surface) facing away (andupward in FIG. 7C) from the hollow interior of the coil cup member 32.The shelf 98 has a surface 99 (extending the inner pole surface 54 (seeFIG. 7A)) facing away (and upward in FIG. 7C) from the hollow interiorof the coil cup member 32. The addition of shelves 58 and 98 providesthe advantages described above regarding FIGS. 7A and 7B.

In the embodiments of the present invention shown in FIGS. 3A and 3B,the minimum amount of spacing that may be provided between the outer andinner poles is determined by the distance between the outer and innerpoles where fringing occurs, i.e., where the electromagnetic flux maybridge the gap between the inner and outer poles. Thus, although it isdesirable to increase the areas of the poles, a minimum distance or gapmust be maintained between the inner and outer poles to avoid fringing.The large surface area of the straight edges of the inner and outerpoles that are opposed one to another may increase the likelihood thatfringing will occur for a particular spacing between the inner and outerpoles. This is because the straight edges have a large amount of surfacearea over which fringing may occur.

Thus, according to further embodiments of the present inventionillustrated in FIGS. 3C and 3D, the inner edges of shelves 58 and 98 maybe angled in order to minimize the straight surface area of the innerand outer poles that are opposed one to another in order to reduce thepossibility that electromagnetic flux will bridge the gap between theinner and outer poles. Thus, a smaller gap between the inner and outerpoles may be achieved.

FIG. 3C shows the shelf 58 of FIG. 3A with an angled edge. FIG. 3D showsthe shelves 58 and 98 of FIG. 3B with angled edges. The edges may beformed at any suitable angle. According to embodiments of the presentinvention, the angle of the edge may be between approximately 10 degreesand 20 degrees. In the embodiment shown in FIG. 3D either or both of theshelves may have angled edges.

The coil cup member 32, including the shelf 58 and/or 98, is preferablymade of a generally rigid material, having a relatively high magneticpermeability such as, but not limited to, low carbon steel, iron,nickel, ferritic stainless steel, ferrite, other ferrous materials,combinations thereof, or the like. As described in further detail below,at the open end of the cup member, the surfaces 54 and 59 of the hub 51and shelf 58 (FIG. 7A) and/or surfaces 54 and 99 of the hub 51 and shelf98 (FIG. 7B) define pole surfaces that cooperate with pole surfaces onan armature to provide a path for electromagnetic flux during a forwardstroke of the drive mechanism.

The shelf 58 (and/or 98) of the coil cup member 32 may be formed as aseparate, annular element, that is secured to outer wall 56 (and/or hub51) of the coil cup member 32 by any suitable means, including, but notlimited to, interference fitting, adhesive, welding, brazing or thelike. By forming the shelf 58 (and/or 98) separately, the manufacturingstep of placing the coil 34 in the coil cup member 32 may be simplified,because the coil 34 may be placed within the interior of the coil cupmember 32, before the shelf 58 (and/or 98) is secured to the outer wall56 (and/or hub 51). Alternatively, the shelf 58 (and/or 98) may beformed as a unitary body with the rest of the coil cup member 32, forexample, in a molding or machining process.

When assembled in the pump drive mechanism, the coil cup member 32 islocated in the hollow interior of the housing member 30, with thecentral hub portion 42 of the housing 30 extending through the centralchannel 52 of the coil cup 32, as shown in FIGS. 3A-D and 4A-D. The coil34 is located within the hollow, annular interior of the coil cup member32, and is disposed around the axis A of the annular interior of thecoil cup member 32. The coil cup member 32 is provided with an opening60, through which coil leads extend, as shown in FIGS. 3A-D and 4A-D.

The coil 34 comprises a conductive wire wound in a coil configuration.The coil wire may comprise any suitable conductive material such as, butnot limited to, silver, copper, gold or the like, with each turnelectrically insulated from adjacent turns and the housing. In onepreferred embodiment, the coil wire has a square or rectangularcross-section, to allow minimal space between windings, thereby to allowa greater number of coil turns and, thus, improved electricalefficiency.

A biocompatible and infusion medium compatible barrier 61 may be locatedover the open side of the coil cup 32, between the armature portion 62and the coil cup member 32, to maintain a gap between those two membersand/or to help seal the annular interior of the coil cup and coil 34. Inother embodiments in which infusion medium may contact the coil, thebarrier 61 may be omitted.

Actuator Member For Drive Mechanism

A perspective view of an example embodiment of an actuator member 36 forthe drive mechanism 20 is shown in FIG. 8. Other example embodiments ofactuator members are described below with reference to FIGS. 10-12. Theactuator member 36 shown in FIG. 8 is configured to operate with a coilcup member 32 having a shelf portion 58 (and/or 98) such as describedabove with respect to the example embodiments of FIGS. 7A, 7B and 7C.However, actuator member embodiments described below with respect toFIGS. 10- 12 may be configured either to operate with a coil cup member32 having a shelf portion 58 (and/or 98) as described above with respectto FIGS. 7A, 7B and 7C, or with a coil cup member configuration havingno shelf portion as described in the above-referenced U.S. patentapplication Ser. No. 10/033,724.

With reference to the example embodiment shown in FIG. 8, the actuatormember 36 has an armature portion 62 and a piston portion 64. In theexample embodiment of FIG. 8, the armature portion 62 and the pistonportion 64 of the actuator are fixed together and may be formed as asingle unitary actuator structure. However, other actuator embodimentsdescribed below (with respect to FIG. 11) may employ a piston portionthat is separable from the armature portion. As shown in FIG. 8, thearmature portion 62 of the actuator member has a generally round, discshaped configuration, with an annular outer section (or outer pole) 66and an annular inner section (or inner pole) 65. The area of the innerand outer pole surfaces may be selected for optimal efficiency. Forexample, the inner pole surface area may be about 0.02937 square inches,while the outer pole surface area may be about 0.05347 square inches.Other embodiments may employ other suitable pole surface areas.

As described in more detail below, the armature portion 62 cooperateswith the pole surfaces 54, 59 and/or 99 of the coil cup member 32, toprovide a flux path for electromagnetic flux. In addition, the armatureportion 62 of the actuator 36 is located in a volume of the pumpmechanism 20, in which it is in direct contact with infusion medium tobe pumped to the patient. Accordingly, the armature portion 62 of theactuator 36 is preferably made of a generally rigid material, having arelatively high magnetic permeability such as, but not limited to,ferrous materials such as S44700 stainless steel (ASTM A276-98b) or thelike.

In addition, in preferred embodiments, the ferrous material of thearmature portion 62 is suitably covered with a biocompatible andinfusion medium compatible material, such as titanium or titanium alloycladding. Titanium can exhibit a relatively high level of corrosionresistance and compatibility with a large variety of infusion media.Accordingly, embodiments of the invention may employ a titanium ortitanium alloy coating on the armature portion (and other portions ofthe pump drive mechanism that come into direct contact with the infusionmedium), to allow operation with any one of a variety of different typesof infusion media. For example, embodiments of the invention may employa layer of about 1.5 mils to about 3.0 mils of titanium or titaniumalloy on a ferrous armature portion 62. However, other embodiments mayemploy other suitable cladding thicknesses and other suitable coatingmaterials that provide a sufficient resistance to and compatibility witha variety of types of infusion media, including, but not limited to,carbon coating, gold, platinum, diamond, titanium nitride or otherceramic material. Such coatings may be applied in any suitable manner,including, but not limited to electrochemical or electromagneticdeposition, dipping or applying liquid cladding materials that solidifyon the actuator, or the like.

In one example embodiment (not shown), the armature portion 62 of theactuator member 36 is provided with a plurality of apertures and radialstruts as described in further detail in the above-referenced U.S.patent application Ser. No. 10/033,722. Such apertures allow thearmature portion of the actuator to move within a volume of fluidicinfusion media with reduced resistance from the fluid (by allowing fluidto pass through the apertures during actuator movement). The radialstruts complete the flux path between the inner and outer poles of thearmature portion 62.

However, such apertures and struts in the armature portion can increasethe manufacturing complexity, especially if the magnetically permeablematerial of the armature portion 62 is to be clad with a titanium,titanium alloy or other suitable cladding material. In particular, itcan be difficult to sufficiently clad all exposed surfaces of anarmature portion having such apertures and radial struts. Accordingly,further embodiments employ an armature portion 62 that is free ofapertures and radial struts. Yet other embodiments employ a relativelysmall number of apertures.

Without apertures (or with a reduced number of apertures), the problemsassociated with fluidic resistance and stirring of the infusion medianoted above may be encountered. Accordingly, embodiments employingarmature portions 62 with no or minimal apertures are preferablyconfigured with a reduced diameter. The reduced diameter of the armatureportion 62 results in less fluidic resistance, because the armature hasless surface area in contact with the infusion medium and displaces lessvolume of the infusion medium during actuator movement. Alternatively,instead of reducing the armature diameter, the diameter dimensions ofthe coil, coil cup member and housing may be increased relative to thediameter of the armature portion 62, to increase electromagnetic powerapplied to the armature. However, such an alternative embodiment mayresult in increased power consumption and increased dimensions of thepump mechanism. Thus, embodiments employing a reduced diameter armatureportion 62 may be preferred in implant environments, in which minimizingsize and maximizing power usage efficiency are typically important.

According to further embodiments of the present invention, the armatureportion 62 of the actuator 36 may be manufactured from any suitablematerial, including materials having a low magnetic permeability.According to these embodiments, as shown in FIGS. 14A, 14B and 15,armature portion 62 of the actuator 36 may be formed with a cavity 117into which a material 119 may be placed. Material 119 may be anysuitable material having a relatively high magnetic permeability suchas, but not limited to, ferrous materials such as S44700 stainless steelor the like. A cover 121 made from a material such as, but not limitedto, a foil material, may then be placed over the cavity 117 to provide acover for material 119. FIG. 14A shows armature portion 62, material 119and cover 121 in an unassembled state. FIG. 14B shows armature portion62, material 119 and cover 121 in an assembled state. FIG. 15 shows anassembled actuator 36 (including the armature portion 62 and the pistonportion 64) having a cavity 117 into which a material 119 is placed andcovered with cover 121, according to an embodiment of the presentinvention. The material 119 may be chosen to have any suitabledimensions.

By providing a cavity in the armature portion 62 of the actuator 36 inwhich to place and cover the relatively high magnetic permeabilitymaterial, contact between the relatively high magnetic permeabilitymaterial and the infusion medium is minimized. The relatively highmagnetic permeability material provides a flux path for electromagneticflux, so that the remainder of the armature portion 62 need not do so.Thus, the remainder of the armature portion 62 may be manufactured fromany suitable biocompatible and infusion medium compatible material,having no or low magnetic permeability such as, but not limited to,titanium, stainless steel (which may be ferritic or non-ferritic),biocompatible plastic, ceramic, glass or the like.

When assembled (as shown in FIGS. 3A-D and 4A-D), the armature portion62 of the actuator member 36 resides adjacent the open end of the coilcup member 32 and the piston portion 64 of the actuator member 36extends into the piston channel 44 of the housing member 30. Asdescribed above, the armature portion 62 of the actuator member 36includes a magnetically permeable material. This allows the armature toelectromagnetically cooperate with the coil cup member 32 and form aflux path, upon electrical energization of the coil 34.

More specifically, the armature portion 62 is provided with an annularinner pole surface 65 and an annular outer pole surface 66. In theillustrated embodiments, the annular pole surfaces 65 and 66 are raisedrelative to the rest of the armature portion 62, for example, to allowfor a greater amount of magnetically permeable material to be present atthe pole locations. However, in other embodiments, the pole surfaces maybe in plane with the rest of the armature portion or recessed relativeto the rest of the armature portion.

A simplified, cross-sectional diagram of the coil cup member 32 and theactuator member 36 illustrated in FIG. 3A, in their assembledorientation, is shown in FIG. 9. As described in more detail below, theinner and outer pole surfaces 65 and 66 of the armature portion 62 alignwith the inner and outer pole surfaces 54 and 59 of the coil cup member32 to allow a flux path F to be formed, when the coil 34 is energized.Upon energization of the coil 34, the flux path F is formed through theouter peripheral wall 56 of the coil cup member 32 and across a gapbetween the outer pole surface 59 of the coil cup member 32 and theouter pole surface 66 of the armature portion 62. The flux path Fcontinues through the armature portion 62, across the gap between theinner pole surface 65 of the armature portion 62 and the inner polesurface 54 of the coil cup member 32. The circuit of the flux path F iscompleted through the hub portion 51 and backiron 57 of the coil cupmember 32, and back to the outer peripheral wall 56 of the coil cupmember 32. Although not described in detail, embodiments of the presentinvention illustrated in FIGS. 3B-D operate in a similar manner to thatdescribed for the embodiment illustrated in FIG. 3A.

As shown in FIG. 9, by employing a coil cup member 32 with a shelf 58extending toward the hub 51, the outer pole 66 of the armature portion62 need not extend to the outer wall 56 to provide the flux path F.Instead, a portion of the flux path F can be provided through the shelf58. In this manner, the diameter D of the armature portion 62 may beminimized, for example, to simplify manufacturing processes, reducestirring of infusion media during actuator movement and/or make moreefficient use of power. Alternatively, the shelf 58 may be employed toallow the diameter of the coil cup member 32 to be increased, withoutrequiring a like increase in the diameter of the armature portion 62.

In the embodiment shown in FIG. 9, the relative dimensions of thearmature portion 62, coil cup member 32 and shelf 58 are selected suchthat the outer pole 66 of the armature portion 62 overlaps a portion ofthe shelf 58. A gap is provided between the outer pole 66 of thearmature portion 62 and the shelf 58. Similarly, a gap is providedbetween the inner pole 65 of the armature portion 62 and the inner polesurface 54 of the coil cup member 32.

In some embodiments, the armature portion 62 and/or the coil cup member32 may be configured such that the gap between the outer pole surface 66of the armature portion 62 and the outer pole surface 59 of the coil cupmember 32 is greater than the gap between the inner pole surface 65 ofthe armature portion 62 and the inner pole surface 54 (FIG. 7A) of thecoil cup member, when the actuator is in the retracted position shown inFIGS. 3A-D. A greater outer pole spacing, relative to the inner polespacing, can result in reduced residual flux that could otherwise causethe armature to stick in the forward position (the FIGS. 4A-D position).In addition, a greater outer pole spacing reduces the squeezing effecton infusion medium between the outer pole 66 of the armature portion 62and the shelf 58, as the armature portion 62 moves toward the forwardposition during actuation of the pump mechanism.

As described in more detail below, the energization of the coil 34creates an electromagnetic force on the armature portion 62 of theactuator 36, to draw the armature portion 62 toward the coil cup member32 (i.e., to close the gaps between the inner pole surfaces 54 and 65and between the outer pole surfaces 59 and 66). By drawing the armatureportion 62 of the actuator member 36 toward the coil cup member 32, thepiston portion 64 of the actuator member 36 is forced further into thepiston channel 44, toward the outlet chamber of the housing member 30.This action effects a forward stroke of the drive mechanism 20, as shownin FIGS. 4A-D. Upon sufficient de-energization of the coil 34, theactuator member 36 is forced toward a retracted position, as shown inFIGS. 3A-D, for example, by the force of a spring 68, a magnet (notshown) or both.

The actuator spring 68 in the illustrated embodiment comprises a coilspring disposed around the piston portion 64 of the actuator member 36,adjacent the armature portion 62 of the actuator member 36. One end ofthe coil spring abuts the armature portion 62 of the actuator, while theopposite end of the coil spring abuts a shoulder 70 in the pistonchannel 44 of the housing member 30. In this manner, the actuator spring68 imparts a spring force between the housing member 30 and the actuatormember 36, to urge the actuator member 36 toward its retracted positionshown in FIG. 3A-D.

In the illustrated embodiment, by using a coil spring 68 located aroundand coaxial with the piston portion 64 and disposed partially within thepiston channel 44, the actuator spring may have minimal or nocontribution to the overall thickness dimension of the drive mechanism.However, in other embodiments, actuator springs may have other suitableforms and may be located in other positions suitable for urging theactuator toward its retracted position shown in FIGS. 3A-D. The actuatorspring 68 is preferably made of a biocompatible and infusion mediumcompatible material that exhibits a suitable spring force such as, butnot limited to, titanium, stainless steel, MP35N cobalt steel or thelike. In further embodiments, a magnet may be arranged to provide areturn force on the actuator, either in addition to or as an alternativeto the actuator spring 68, to return the actuator to its retractedposition. An example of a magnet arranged for providing a return forceon an actuator is described in U.S. patent application Ser. No.10/033,724.

Cover Member for Drive Mechanism

The cover member 38 of the drive mechanism 20 attaches to the housingmember 30, to cover the open side of the housing member, the armatureportion 62 and the barrier 61. The cover member 38 is preferably made ofa generally rigid, biocompatible and infusion medium compatiblematerial, having a relatively low magnetic permeability (beingrelatively magnetically opaque) such as, but not limited to, titanium,stainless steel, biocompatible plastic, ceramic, glass or the like.

The cover member 38 defines an interior volume 72 between the barrier 61and the inner surface of the cover member. The armature portion 62 ofthe actuator member 36 resides within the interior volume 72 when thecover is attached to the housing, as shown in FIGS. 3A-D and 4A-D. Asdescribed below, the armature portion 62 of the actuator 36 is moveablein the axial direction A within the volume 72, between a retractedposition shown in FIGS. 3A-D and a forward stroke position shown inFIGS. A-D. This movement is created by the action of electromagneticforce generated when a current is passed through the coil 34 and by themechanical return action of the actuator spring 68.

An adjusting plunger 74 may be located within the cover member 38, forcontacting the armature portion 62 of the actuator 36, when the armatureportion 62 is in the fully retracted position shown in FIGS. 3A-D. Theadjusting plunger 74 may be used to set the retracted position of thearmature portion 62. A seal may be disposed between the plunger 74 andthe cover member 38, for example, but not limited to, a silicon rubbersealing ring. In further embodiments, a flexible diaphragm 76 (such as,but not limited to, a thin titanium sheet or foil) may be coupled to theinside surface of the cover member 38 and sealed around the openingthrough which the plunger 74 extends. The diaphragm will flex to allowthe plunger to define an adjustable retracted position and, yet, providesealing functions for inhibiting leakage at the interface between theplunger 74 and the cover member 38. In further embodiments, once aproper armature position is set, the plunger may be fixed in place withrespect to the cover member, for example, by adhering the plunger to thecover member with one or more welds, adhesives or other securingmethods.

The cover member 38 includes the inlet 26 of the drive mechanism, whichhas an inlet opening 78 in fluid flow communication with the interiorvolume 72. The inlet opening 78 connects in fluid flow communicationwith the reservoir of the infusion device 10 (FIG. 1), to receiveinfusion medium from the reservoir. Connection of the inlet opening 78and the reservoir may be through suitable conduit (not shown), such astubing made of or coated with suitable infusion medium compatiblematerial, including, but not limited to titanium, stainless steel,biocompatible plastic, ceramic, glass or the like. In a furtherembodiment, the tubing is made of or coated with a material selected tobe compatible with a variety of infusion media, such as, but not limitedto titanium, titanium alloy, stainless steel, or the like.

Piston Channel and Outlet Chamber for Drive Mechanism

As shown in FIGS. 3A-D and 4A-D, the piston portion 64 of the actuatormember 36 extends through the axial piston channel 44 in the housingmember 30, toward the outlet chamber 48 at the end of the piston channel44. The channel 44 has an inside diameter which is larger than theoutside diameter of the piston portion 64. As a result, an annularvolume is defined between the piston portion 64 and the wall of thepiston channel 44, along the length of the piston channel 44. Infusionmedium may flow through the annular volume, from the volume 72 withinthe cover member 38 to a piston chamber 80 located between the free endof the piston portion 64 and a valve member 82 of a valve assembly 84.

In some example embodiments of the invention, the radial spacing betweenthe piston portion 64 and the wall of the piston channel 44 is selectedto be large enough to provide a suitable flow of infusion medium towardthe pumping chamber 80 to refill the pumping chamber 80 (during a returnstroke of the piston portion), but small enough to sufficiently inhibitback flow of medium from the pumping chamber 80 (during a forward strokeof the piston portion).

The actual radial spacing between the piston portion 64 and the wall ofthe channel 44 to achieve such results depends, in part, on the overalldimensions of those components, the pressure differentials created inthe mechanism and the viscosity of the infusion medium. For example, theradial spacing may be selected such that the volume of medium forrefilling is between about 1 and 4 orders of magnitude (and, morepreferably, about 2 orders of magnitude) greater than the volume ofmedium that backflows through the space. Alternatively, or in addition,the radial spacing may be defined by the ratio of the diameter D_(P) ofthe piston portion 64 the diameter D_(C) of the channel 44, where theratio D_(P)/D_(C) is preferably within a range of about 0.990 to about0.995. As a representative example, a total spacing of about 400 to 600micro-inches or less and, preferably, an average radial gap of about 250micro-inches annularly around the piston portion 64 may be employed. Infurther embodiments described below with reference to FIGS. 10-12, otherrelative dimensions between the piston portion and pumping channel maybe employed.

The valve assembly 84 in the embodiment of FIGS. 3A-D and 4A-D includesthe valve member 82, a valve spring 83 and support ring 85. The valvemember 82 is located within the outlet chamber 48 and, as shown in FIGS.3A-D, is positioned to close the opening between the axial pistonchannel 44 and the outlet chamber 48, when the actuator member 36 is inthe retracted position. In FIGS. 4A-D, the valve member 82 is positionedto open a flow passage between the axial piston channel 44 and theoutlet chamber 48. The valve spring 83 is located within the outletchamber 48, to support the valve member 82. The spring 83 imparts aspring force on the valve member 82, in the direction toward piston 64,urging the valve member 82 toward a closed position, to block theopening between the axial channel 44 and the outlet chamber 48.

The valve member 82 and the support ring 85 are preferably made of agenerally rigid, biocompatible and infusion medium compatible material,such as, but not limited to, titanium, stainless steel, biocompatibleplastic, ceramic, glass, gold, platinum or the like. In a furtherembodiment, the valve member and ring are made of or clad with amaterial selected to be compatible with a variety of infusion media,such as, but not limited to titanium or titanium alloy, or the like.

A layer of silicon rubber or other suitable material may be attached tothe rigid valve member material, on the surface facing the channel 44,to help seal the opening to the channel 44 when the valve member is inthe closed position shown in FIGS. 3A-D. Various alternative valveassembly configurations may be employed with embodiments of the presentinvention, including, but not limited to such configurations asdescribed in co-pending U.S. patent application Ser. No. 10/033,722.

The valve spring 83 is preferably made of a biocompatible and infusionmedium compatible material that exhibits a suitable spring force suchas, but not limited to, titanium, stainless steel, MP35N cobalt steel orthe like. In a further embodiment, the spring is made of or clad with amaterial selected to be compatible with a variety of types of infusionmedia, such as, but not limited to titanium, titanium alloy, stainlesssteel, or the like.

In the illustrated embodiment, the outlet chamber 48 comprises a cavityin the bottom of the housing 30, as shown in FIGS. 3A-D and 4A-D. Theoutlet chamber cavity 48 may be provided in flow communication with anoutlet 28 (FIG. 2), through a flow passage (not shown). The outlet flowpassage may include one or more accumulator cavities provided withaccumulators, as described in the above-referenced U.S. patentapplication Ser. No. 10/033,722, for example, to help stabilize the flowrate of the drive mechanism, help provide a relatively constant outputpressure during drive operations, and minimize backflow down axialchannel 44.

Manufacturing Process for Drive Mechanism

A drive mechanism as shown in FIGS. 3A-D and 4A-D may be constructed byproviding components as shown in FIG. 5 and assembling the components inany suitable sequence. The components may be made according to anysuitable process including, but not limited to molding, machining,extruding, sintering, casting, combinations thereof or the like.

The coil 34 may be inserted into the annular interior of the coil cupmember 32, with the coil leads extended through a coil lead opening 60in the coil cup. The coil may be impregnated or partially impregnatedwith a fill material of epoxy or the like, for adhering the coil to thecoil cup and for sealing or partially sealing the coil. The fillmaterial may also be used to adhere the barrier plate 61 to the coilmembers, to avoid warping or bulging of the barrier plate afterassembly.

The coil cup member 32 and coil 34 may be inserted into the interior 40of the housing member 30, with the coil leads or connectors (which maybe wire leads or flexible conductive tabs) extending through a coil leadopening 46 in the housing member 30. In preferred embodiments, the coilcup and housing members are configured to provide a tight, friction fittherebetween, without requiring additional means of adhering the twocomponents together. In other embodiments, the coil cup and housingmembers may be coupled together by any suitable adhesive material orother adhering methods, including, but not limited to welding, brazing,of the like.

The barrier 61 may be placed over the coil, coil cup and housingsub-assembly. The barrier 61 may be adhered to the housing by one ormore adhering points or continuously along the circumference of thebarrier 61, with any suitable adhesive material or other adheringmethods, including, but not limited to welding, brazing, soldering orthe like. Alternatively, or in addition, the barrier 61 may be held inplace by a shoulder portion of the, cover member 38. In addition, asnoted above, the barrier 61 may be adhered to the coil 34 by fillmaterial in the coil. In preferred embodiments, the barrier 61 is heldin a generally flat relation relative to the coil cup member and coil.To enhance this flat relation, the coil cup and housing members mayassembled together and then machined to planarize the barrier contactsurfaces, prior to inserting the coil in the coil cup and prior toadding fill material to the coil.

Once the barrier 61 is placed over the coil, coil cup and housingmembers, the actuator member 36 may be added to the sub-assembly. First,however, the actuator spring 68 is placed around the piston portion 64,adjacent the armature portion 62 of the actuator member 36. Then thefree end of the piston portion 64 is inserted into the axial channel 44of the housing member 30, with the armature end of the actuator member36 arranged adjacent the barrier 61.

The cover member 38 may then be disposed over the armature end of theactuator member 36 and secured to the housing member 30. In preferredembodiments, the cover member 38 is adhered to the housing member 30 byone or more adhering points or continuously along the circumference ofthe cover member 38, with one or more welds or any other suitableadhering methods, including, but not limited to adhesive materials,brazing or the like.

The valve side of the drive mechanism may be assembled before or afterthe above-described components are assembled. On the valve side of thedrive mechanism, the valve member 82 is disposed within the outletchamber cavity 48 of the housing member 30. The valve spring 83 and ring85 are disposed within the outlet chamber cavity 48, adjacent the valvemember 82. Any suitable number of accumulators may be placed within eachof the accumulator cavities (not shown). A valve cover 86 may then beplaced over the outlet chamber cavity 48 and accumulator cavities. Thevalve cover 86 may be adhered to the housing member 30 by one or moreadhering points or continuously along the circumference of the valvecover, with one or more welds or any other suitable adhering methods,including, but not limited to adhesive materials, brazing or the like.

The volume of the pumping chamber 80, the compression of the actuatorspring 68 and the position of the actuator 36 in the retracted positionshown in FIGS. 3A-D may be adjusted by the adjusting the position of theadjusting plunger 74. Adjustments of the plunger 74 may be made duringmanufacture and the adjusted position may be fixed by welding orotherwise adhering the plunger 74 in the adjusted position duringmanufacture. In other embodiments, the plunger 74 is not set and weldedduring manufacture, to allow adjustment of plunger 74 after manufacture.

Operation Of Drive Mechanism

In operation, the drive mechanism 20 employs electromagnetic andmechanical forces to move between retracted (FIGS. 3A-D) and forward(FIGS. 4A-D) positions, to cause infusion medium to be drawn into anddriven out of the mechanism in a controlled manner. In the retractedposition, the spring 68 urges the actuator 36 toward its retractedposition shown in FIGS. 3A-D. When the coil 34 is energized to overcomethe spring force of spring 68, the actuator 36 moves to its forwardstroke position shown in FIGS. 4A-D. The movement of the actuatorbetween retracted and forward positions creates pressure differentialswithin the internal chambers and volumes of the drive mechanism 20 todraw medium into the inlet 26 and drive medium out the outlet 28.

More specifically, when the coil 34 is de-activated (not energized ornot energized in a manner to overcome the spring force of spring 68),the actuator 36 is held in its retracted position (FIGS. 3A-D) under theforce of the spring 68. When the coil is de-activated immediatelyfollowing a forward stroke, the spring 68 moves the actuator 36 to theretracted position of FIGS. 3A-D, from the forward position shown inFIGS. 4A-D.

As the actuator 36 retracts, the piston portion 64 of the actuator isretracted relative to the valve member 82, such that a pumping chamber80 volume is formed or expanded between the end of the piston portion 64and the valve member 82. The formation or expansion of the pumpingchamber 80 volume creates a negative pressure which draws infusionmedium from the volume 72 of the cover member 38, through the annularspace between the piston portion 64 and the wall of the piston channel44, and into the pumping chamber 80. While not shown in FIGS. 3A-D,other embodiments (such as shown in FIGS. 10- 12) may include one ormore channels through the piston portion 64, to provide one or moreadditional flow paths to the pumping chamber 80.

In the retracted position, a gap is formed between each of the annularinner and outer pole surfaces 54 and 59 on the coil cup member 32 and arespective annular surfaces of the inner and outer pole surfaces 65 and66 on the armature portion 62 of the actuator member 36. In particular,with reference to FIGS. 3A-D, gaps are formed between the annular polesurfaces of the coil cup member 32 and the armature portion 62 of theactuator member 36.

When the coil 34 is energized (or energized sufficiently to overcome thespring force of spring 68), the actuator member 36 is forced in thedirection to close the gaps between the pole surfaces and moves to itsforward position (FIGS. 4A-D) under the influence of electromagneticflux generated by the energized coil. In particular, the coil 34 may beenergized by passing an electrical current through the coil conductor tocreate electromagnetic flux. The electromagnetic flux defines a fluxpath F as described above with respect to FIG. 9. The electromagneticflux provides an attraction force between the annular pole surfaces 54and 59 of the coil cup member 32 and the annular pole surfaces 65 and 66of the armature portion 62 of the actuator member 36, to draw thearmature portion 62 toward the coil cup member 32.

As the armature portion 62 of the actuator member 36 is drawn toward thecoil cup member 32, the piston portion 64 of the actuator member 36 ismoved axially through the channel 44, in the direction toward the outletchamber 48. With the coil energized, the piston portion 64 continues tomove under the action of the armature, until a mechanical stop isreached, for example, mechanical contact of the armature portion 62 ofthe actuator 36 with the barrier 61, a portion of the housing member 30or cover member 38. In other embodiments, the motion may continue untilthe return force of the spring 68 and fluid pressure inhibits anyfurther forward motion from the electromagnetic force of the energizedthe coil.

The movement of the piston portion 64 towards the stopping point reducesthe volume of the pumping chamber 80 and increases the pressure withinthe piston chamber until the pressure is sufficient to overcome theforce of the valve spring 83. As the valve spring force is overcome bythe pressure within the piston chamber, the valve member 82 is movedtoward an open position, away from the opening between the pumpingchamber 80 outlet chamber 48. When the valve member 82 is in the openposition, medium is discharged through the outlet chamber 48 and,eventually, through outlet 28 (FIG. 2). When the coil is deactivated andthe piston portion 64 is moved back to its retracted position, thepressure in the pumping chamber 80 reduces and the valve member 82 isreseated under the action of the valve spring 83. This inhibits fluidfrom flowing back into the drive mechanism, through the outlet. Inaddition, a negative pressure is created in the pumping chamber 80 todraw medium into the chamber for the next forward stroke, as describedabove.

In this manner, energization of the coil 34 to move the actuator member36 from its retracted position (FIGS. 3A-D), to its forward position(FIGS. 4A-D), causes a measured volume of medium to be discharged fromthe outlet. As described above, when the coil 34 is de-energized, theactuator member 36 is returned to the retracted position (FIGS. 3A-D)under the force of spring 68 and an additional volume of medium is drawninto the pumping chamber 80 for the next discharging operation.Accordingly, the coil 34 may be energized and de-energized by acontrolled electronic pulse signal, where each pulse may actuate thedrive mechanism 20 to discharge a measured volume of medium. Inpreferred embodiments, the coil 34 may be electrically coupled to anelectronic control circuit (not shown) to receive an electronic pulsesignal from the control circuit for example, in response to a sensorsignal, timer signal or other control signal input to the controlcircuit.

In preferred embodiments, when the piston motion is stopped at the endof the forward stroke, the valve-facing end of the piston portion 64 isin close proximity to the valve member 66, for example, spaced from thevalve member 82 by no more than about ten percent (10%) of the pistonstroke. In further embodiments, the valve facing end of the pistonportion 64 is in contact with the valve member 82, at the end of theforward stroke. In this manner, gas that may be present in the infusionmedium is less likely to accumulate within the pumping chamber 80. Morespecifically, in some operational contexts, infusion medium may containgas in the form of small bubbles that may migrate into the pumpingchamber 80 during filling of the piston chamber. As gas is significantlymore compressible than liquid, too much gas within the pumping chambermay adversely affect the ability of the drive mechanism to self prime.

In yet another embodiment the piston portion 64 may contact the valvemember 82 at the end of the forward stroke and push the valve member 82open. In this embodiment, it is less likely that gas will be trappedbetween the piston portion 64 and the valve member 82, and more likelythat the chamber will be purged of gas.

Further Drive Mechanism Embodiments

In the embodiments described above, movement of the actuator 36 to theretracted position (FIGS. 3A-D) causes the piston portion 64 of theactuator to retract, such that a pumping chamber 80 volume is formed orexpanded between the end of the piston portion 64 and the valve member82. The formation or expansion of the pumping chamber 80 volume createsa negative pressure which draws infusion medium from the volume 72 ofthe cover member 38, through the annular space between the pistonportion 64 and the wall of the piston channel 44, and into the pumpingchamber 80.

The rate at which the infusion medium fills the pumping chamber 80 candepend upon various factors, including the viscosity of the infusionmedium and the width of the

annular space between the piston portion 64 and the wall of the pistonchannel 44. To accommodate a greater variety of infusion media and,thus, a greater range of viscosities, embodiments of the invention mayemploy a piston portion 64 and piston channel 44 configured to improvethe flow of an infusion medium into the pumping chamber 80. Suchconfigurations may include one or more of the features described belowwith respect to FIGS. 10-12.

FIG. 10 shows an embodiment of an actuator member 36′ having an armatureportion 62′ and a piston portion 64′, similar in many respects to thearmature portion 62 and piston portion 64 of the actuator member 36described above. However, the actuator member 36′ is configured with acentral channel 90 extending through the armature portion 62′ and theaxial length of the piston portion 64′. The channel 90 has openings 92and 93 on the armature and piston ends of the actuator member 36′. Whenthe actuator member 36′ is employed in a pump drive mechanism 20 asshown in FIGS. 3A-D and 4A-D, the channel 90 allows the infusion mediumto flow from the cover volume 72, through the piston portion 64′ andinto the pumping chamber 80. Thus, as the actuator member 36′ movestoward a retracted position (the FIGS. 3A-D position of the actuatormember), fluidic infusion medium flows through the channel 90 and intothe pumping chamber 80.

A valve structure 94 may be provided to control the flow of fluidthrough the channel 90. For example, a valve structure 94 may beconfigured to restrict or inhibit a reverse flow of infusion medium fromthe pumping chamber 80 and back through the channel 90, toward the covervolume 72, during forward strokes of the actuator. In one embodiment,the valve structure may comprise a ball-shaped plug located in a taperedvolume, for selectively blocking the flow of infusion medium through thechannel 90, as shown in FIG. 10. In other embodiments, other suitablevalve configurations may be employed, including, but not limited to acone-shaped plug in a larger cone-shaped volume, or the like.

The valve structure 94 may be located within the channel 90, forexample, adjacent the piston chamber opening 93 of the channel 90.Alternatively, the valve structure 94 may be located in other suitablepositions along the length of the channel 90. In further embodiments,the valve structure may include a ball (or other shaped plug) locatedwithin the pumping chamber 80, for selectively blocking the opening 93of the channel 90. In such further embodiments, the opening 93 of thechannel 90 may be shaped to cooperate with the shape of the ball (orother shaped plug), to provide a sealing or partial sealing functionagainst back flow of the infusion medium. Thus, for example, the opening93 may be tapered inward, cone-shaped or the like, to provide a seat forthe ball (or other shaped plug) within the pumping chamber 80. In yetfurther embodiments, multiple valve structures may be located, forexample, along the length of the channel 90, at the opening 92, at theopening 93 and/or within the pumping chamber 80, as described above.

During each forward stroke of the actuator member 36′, the valvestructure 94 closes and the infusion medium is restricted or inhibitedfrom flowing from the pumping chamber 80, through the channel 90, towardthe cover volume 72, for example. However, as the actuator member 36′ ismoved back toward a retracted position, the valve structure 94 opens andallows the infusion medium to flow from the cover volume 72, through thechannel 90 and into the pumping chamber 80. In this manner, the channel90 and valve structure 94 provide a controlled flow path, for thecommunication of infusion medium into the pumping chamber 80. Moreover,the channel 90 and valve structure 94 may be readily configured withsufficient channel width to allow sufficient filling of the pumpingchamber 80 with any one of a variety of infusion media (and, thus, avariety of infusion medium viscosities).

The flow path provided by the channel 90 may be employed in combinationwith an annular space (described above) between the piston portion 64′and the wall of the piston channel 44, to communicate infusion medium tothe pumping chamber 80. In further embodiments, the channel 90 mayprovide the primary or sole flow path for communication of infusionmedium into the pumping chamber 80. In such further embodiments, theannular space between the piston portion 64′ and the wall of the pistonchannel 44 may be minimized.

While embodiments described above employ a single piece actuator member36′, further embodiments of an actuator with a central channel 90 may beemployed with multi-piece actuator embodiments, such as the 2-pieceactuator member described in U.S. patent application Ser. No.10/033,722, as the “second drive mechanism embodiment and operation.” Insuch embodiments, the armature portion of the actuator member isseparable from the piston portion of the actuator member. For example,the 2-piece actuator member 36″ shown in FIG. 11 includes an armatureportion 62″ and a piston portion 64″, configured as two separablepieces.

A channel 90, as described above, is provided through the piston portion64″, but need not be provided through the armature portion 62″ of theactuator member 36″. A valve structure 94, as described above, may beprovided in the piston portion 64″. Alternatively, or in addition, avalve structure located in the pumping chamber 80 and/or multiple valvestructures as also described above, may be employed with the 2-pieceactuator embodiment of FIG. 11.

In embodiments as shown in FIGS. 12 and 13, an alternative valvestructure may be employed to control a flow of infusion medium from thechannel 90 of the piston to the pumping chamber 80. For example, asshown in FIG. 12, actuator member 36′″ may include a valve structure 96.Valve structure 96 may be configured to restrict or inhibit a reverseflow of infusion medium from the pumping chamber 80 and back through thechannel 90, toward the cover volume 72, during forward strokes of theactuator (FIGS. 4A-D). A more detailed view of one embodiment of valvestructure 96 is shown in FIG. 13.

As shown in FIG. 13, one embodiment of the valve structure 96 maycomprise a cap 103, a seat 105, and a washer 107. According toembodiments of the present invention, seat 105 has a generallyfrusto-conical shape. However, any suitable shape may be used,including, but not limited to, flat and radiused. The tapered end ofseat 105 is coupled to piston portion 64′″. In one embodiment, seat 105is integral with piston portion 64′″. Piston portion 64′″ may be formedto include indented area 109 for receiving a catch of cap 103. Cap 103may be placed over the end of piston portion 64′″ closest to the pistonchamber 80 such that the catch snaps into indented area 109 to securecap 103 to piston portion 64′″. Cap 103 and seat 105 may be made fromany suitable biocompatible material, including, but not limited to,metal and plastic. In one embodiment, cap 103 is made from polysulfone.

Washer 107 is located between cap 103 and seat 105 to provide a sealingfunction for inhibiting leakage at the interface between seat 105 andwasher 107 during forward strokes of the actuator. In this manner,reverse flow of infusion medium is inhibited during forward strokes ofthe actuator. Cap 103 may include an indentation for seating washer 107.Washer 107 may be press fit into the indentation and/or may be securedwithin the indentation by means of a suitable adhesive or the like.Washer 107 may be made from any suitable biocompatible material,including, but not limited to, silicone rubber.

During a forward stroke, seat 105 is sealed against washer 107 due topressure created in pumping chamber 80, and space 111 is formed by theupward movement of the catch within indented area 109. However, duringreverse strokes, washer 107 and seat 105 separate from one another dueto suction (vacuum) created in pumping chamber 80. Thus, when pistonportion 64′″ is in a reverse stroke, suction is applied to cap 103 suchthat cap 103 moves in a direction opposite to the upward movement ofpiston portion 64′″. Space 111 allows catch to move downward withinindented area 109 until the catch comes to a stop against the bottomshoulder of indented area 109. The separation of washer 107 and seat 105allows flow of infusion medium from cover volume 72 through the channel90, into pumping chamber 80 during reverse strokes. In one embodiment,space 111 may be equal to approximately 0.002 inches or about 20% of thestroke of piston portion 64′″. Other suitable dimensions may be used inother embodiments of the valve structure 96.

In yet further embodiments, the annular space between the piston portionof the actuator member 36 and the wall of the piston channel 44 may beincreased relative to the above-described embodiments, to increase therate of flow of infusion medium from the cover volume 72, into thepumping chamber 80. For example, as shown in FIG. 12, an actuator member36′″ may be provided with a piston portion 64′″ having a reduceddiameter relative to the actuator members shown in the above-describedembodiments. In such embodiments, the rate at which a given infusionmedium may flow through the annular space between the piston portion36′″ and the piston channel 44 is increased (relative to embodimentsemploying a larger diameter piston portion). Accordingly, the rate offilling of the piston chamber may be increased, for example, toaccommodate a greater variety of infusion media.

Alternatively, or in addition to employing an actuator member 36′″having a relatively small diameter piston portion 64′″, the diameter ofthe piston channel 44 may be increased, relative to the above-describedembodiments. By employing a relatively small diameter piston portion64′″ and/or a relatively large diameter piston channel 44, the annularspace between the piston portion 64′″ and the piston channel 44 (and,thus, the rate at which a given infusion medium may flow through theannular space) may be similarly increased.

Various features that may be employed in infusion drive mechanisms forimproving operation with a any one of a variety of infusion media aredescribed herein in connection with the embodiment of FIGS. 10-12.Further features that may be employed for improving operation with anyone of a variety of infusion media are described herein in connectionwith FIGS. 3-9. However, it is contemplated that, where possible,features described in connection with one embodiment may be employed inthe other embodiment. For example, the armature and coil cupconfigurations of FIGS. 3-9 may be employed in combination with one ormore of the channel 90, valve configurations 94 and increased annularspacing between the piston portion and piston channel described abovewith respect to FIGS. 10-12. Moreover, embodiments of FIGS. 3-12 may beemployed with single-piece actuator configurations or multi-pieceactuator configurations.

While drive mechanism embodiments described above employ a coaxialarrangement of the coil, piston channel and piston, other embodimentsmay employ a piston and piston channel located between, but not coaxialwith, a plurality of spaced coils. For example three coils may belocated in a spaced relation at three respective corners of a triangle,with the piston channel and piston located in the center of the triangle(surrounded by the three locations of the coils), and with the pistonaxis parallel to the axes of the coils. In further embodiments more thanthree coils may be located at discrete positions spaced around thepiston (at locations surrounding the piston), preferably, equally spacedfrom the piston or otherwise arranged to provide approximately equalforces on the piston.

The foregoing description of the preferred embodiment of the inventionhas been presented for the purposes of illustration and description. Itis not intended to be exhaustive or to limit the invention to theprecise form disclosed. Many modifications and variations are possiblein light of the above teaching.

1.-38. (canceled)
 39. A drive mechanism for an infusion device, thedrive mechanism comprising: a coil arranged to be selectively energized;an armature moveable in response to energizing the coil, the armaturehaving a first pair of pole surfaces; a piston moveable in conjunctionwith the armature in response to energizing the coil, wherein the pistonis moveable in a piston channel for conveying an infusion media; a coilhousing containing the coil, the coil housing composed of a magnetizablematerial and providing a second pair of pole surfaces in a magnetic fluxpath with the first pair of pole surfaces when the coil is energized;wherein the armature comprises an armature body having a cavity and amagnetic material located within the cavity.
 40. A drive mechanism asrecited in claim 39, wherein the armature body is composed of a materialhaving a lower magnetic permeability relative to the magnetic material.41. A drive mechanism as recited in claim 40, wherein the armature bodyis composed of at least one of titanium, stainless steel, biocompatibleplastic, ceramic or glass.
 42. A drive mechanism as recited in claim 40,wherein the armature body is composed of a non-ferritic stainless steel.43. A drive mechanism as recited in claim 39, wherein the magneticmaterial comprises at least one of a ferrous material and an S44700stainless steel material.
 44. A drive mechanism as recited in claim 39,further comprising a cover provided over the cavity of the armaturebody, to cover the magnetic material located within the cavity.
 45. Adrive mechanism as recited in claim 44, wherein the cover comprises afoil material.
 46. A drive mechanism as recited in claim 39, furthercomprising a cover for inhibiting the magnetic material from contactinginfusion media.
 47. A drive mechanism as recited in claim 39, whereinthe magnetic material located within the cavity completes a flux pathwhen the coil is energized.
 48. A drive mechanism as recited in claim47, further comprising a cover for inhibiting the magnetic material fromcontacting infusion media when the coil is energized.
 49. A drivemechanism as recited in claim 48, wherein the cover comprises a foilmaterial.
 50. A drive mechanism as recited in claim 39, wherein thefirst pole surfaces face the same direction.
 51. A method for making adrive mechanism for an infusion device, the method comprising: arranginga coil to be selectively energized; supporting an armature for movementin response to energizing the coil, the armature having an armature bodyand a first pair of pole surfaces; supporting a piston in a pistonchannel for movement in conjunction with the armature in response toenergizing the coil, to convey an infusion media; containing the coil ina coil housing composed of a magnetizable material; arranging the coilcup such that a second pair of pole surfaces on the coil cup are in amagnetic flux path with the first pair of pole surfaces when the coil isenergized; supporting a magnetic material within a cavity in thearmature body for completing the flux path when the coil is energized.52. A method as recited in claim 51, wherein supporting an armaturecomprises supporting an armature having an armature body composed of amaterial having a lower magnetic permeability relative to the magneticmaterial.
 53. A method as recited in claim 51, wherein supporting anarmature comprises supporting an armature having an armature bodycomposed of at least one of titanium, stainless steel, biocompatibleplastic, ceramic or glass.
 54. A method as recited in claim 51, whereinsupporting an armature comprises supporting an armature having anarmature body composed of a non-ferritic stainless steel.
 55. A methodas recited in claim 51, wherein supporting a magnetic material comprisessupporting at least one of a ferrous material and an S44700 stainlesssteel material.
 56. A method as recited in claim 51, further comprisingcovering the magnetic material with a cover provided over the cavity ofthe armature body.
 57. A method as recited in claim 51, furthercomprising covering the magnetic material with a foil disposed over thecavity of the armature body.
 58. A method as recited in claim 51,further comprising covering the magnetic material with a cover thatinhibits the magnetic material from contacting infusion media.
 59. Adrive mechanism as recited in claim 51, wherein supporting an armaturecomprises supporting an armature with the first pole surfaces facing thesame direction.